Ultra wideband communication system, method, and device with low noise reception

ABSTRACT

An ultra-wide band (UWB) waveform receiver with noise cancellation for use in a UWB digital communication system. The UWB receiver uses a two-stage mixing approach to cancel noise and bias in the receiver. Self-jamming is prevented by inverting a portion of the received signal in the first mixer and then coherently detecting the partially and synchronously inverted signal in the second mixer. Since the drive signals on both mixers are not matched to the desired signal, leakage of either drive signal does not jam the desired signal preventing the receiver from detecting and decoding a weak signal.

CROSS REFERENCE TO RELATED PATENT DOCUMENTS

The present document contains subject matter related to that disclosedin commonly owned, co-pending application Ser. No. 09/209,460 filed May14, 1998, entitled ULTRA WIDE BANDWIDTH SPREAD-SPECTRUM COMMUNICATIONSSYSTEM); Ser. No. 09/633,815, filed Aug. 7, 2000 entitled ELECTRICALLYSMALL PLANAR UWB ANTENNA; application Ser. No. 09/563,292, filed May 3,2000 entitled PLANAR UWB ANTENNA WITH INTEGRATED TRANSMITTER ANDRECEIVER CIRCUITS; Application Ser. No. 60/207,225 filed May 26, 2000,entitles ULTRAWIDEBAND COMMUNICATIONS SYSTEM AND METHOD; applicationSer. No. 09/685,198, filed Oct. 10, 2000, entitled ANALOG SIGNALSEPARATOR FOR UWB VERSUS NARROWBAND SIGNALS; Application Ser. No.60/238,466, filed Oct. 10, 2000, entitled ULTRA WIDE BANDWIDTH NOISECANCELLATION MECHANISM AND METHOD); Application Ser. No. 60/217,099filed Jul. 10, 2000 entitled MULTIMEDIA WIRELESS PERSONAL AREA SYSTEMNETWORK (WPAN) PHYSICAL LAYER SYSTEM AND METHOD); application Ser. No.09/685,203, filed Oct. 10, 2000, entitled SYSTEM AND METHOD FOR BASEBANDREMOVAL OF NARROWBAND INTERFERENCE IN ULTRA WIDEBAND SIGNALS;application Ser. No. 09/685,197, filed Oct. 10, 2000, entitled MODECONTROLLER FOR SIGNAL ACQUISITION AND TRACKING IN AN ULTRA WIDEBANDCOMMUNICATION SYSTEM; application Ser. No. 09/684,400, filed Oct. 10,2000, entitled ULTRA WIDEBAND COMMUNICATION SYSTEM WITH LOW NOISE PULSEFORMATION; application Ser. No., 09/685,195, filed Oct. 10, 2000,entitled ULTRA WIDE BANDWIDTH SYSTEM AND METHOD FOR FASTSYNCHRONIZATION; application Ser. No. 09/684,401, filed Oct. 10, 2000,entitled ULTRA WIDE BANDWIDTH SYSTEM AND METHOD FOR FAST SYNCHRONIZATIONUSING SUB CODE SPINS; application Ser. No., 09/685,196, filed Oct. 10,2000, entitled ULTRA WIDE BANDWIDTH SYSTEM AND METHOD FOR FASTSYNCHRONIZATION USING MULTIPLE DETECTION ARMS; application Ser. No.,09/685,199, filed Oct. 10, 2000, entitled A LOW POWER, HIGH RESOLUTIONTIMING GENERATOR FOR ULTRA-WIDE BANDWIDTH COMMUNICATIONS SYSTEMS;application Ser. No. 09/685,202, filed Oct. 10, 2000, entitled METHODAND SYSTEM FOR ENABLING DEVICE FUNCTIONS BASED ON DISTANCE FORMANCE; andapplication Ser. No. 09/685,201, filed Oct. 10, 2000, entitledCARRIERLESS ULTRA WIDEBAND WIRELESS SIGNALS FOR CONVEYING APPLICATIONDATA; application Ser. No. 09/685,205, filed Oct. 10, 2000 entitledSYSTEM AND METHOD FOR GENERATOR ULTRA WIDEBAND PULSES and applicationSer. No. 09/685,200, filed Oct. 10, 2000, entitled LEAKAGE NULLINGRECEIVER CORRELATOR STRUCTURE AND METHOD FOR ULTRA WIDE BANDWIDTHCOMMUNICATION-S SYSTEM, the entire contents of each of which beingincorporated herein by reference

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ultra wideband (UWB) radiocommunication systems, methods and devices used in the system forgenerating and receiving UWB waveforms that include wavelets that aremodulated to convey digital data over a wireless radio communicationchannel using ultra wideband signaling techniques.

2. Description of the Background

There are numerous radio communication techniques to transmit digitaldata over a wireless channel. These techniques include those used inmobile telephone systems, pagers, remote data collection systems, andwireless networks for computers, among others. Most conventionalwireless communication techniques modulate the digital data onto ahigh-frequency carrier that is then transmitted via an antenna intospace.

Ultra wideband (UWB) communications systems transmit carrierless highdata rate, low power signals. Since a carrier is not used, thetransmitted waveforms themselves contain the information beingcommunicated. Accordingly, conventional UWB systems transmit pulses, theinformation to be communicated is contained in the pulses themselves,and not on a carrier.

Conventional UWB communication systems send a sequence of identicalpulses, the timing of which carries the information being communicated,for example, as described by Fullerton and Cowie (U.S. Pat. No.5,677,927). This technique is known as pulse position modulation (PPM).In a PPM scheme, the information in a pulse is obtained by determiningan arrival time of the pulse at a receiver relative to other pulses. Forexample, given an exemplary time window, if a pulse is received at thebeginning of that time window, the receiver will decode that pulse as a‘1,’ whereas if the pulse is received at the end of that same timewindow, the receiver will decode that pulse as a ‘0.’

Several problems arise with this technique, however, as recognized bythe present inventors. First, it is not as efficient as othertechniques, for example, sending non-inverted and inverted pulses where3 dB less radiated power is required to communicate in the samememory-less Gaussian white noise channel. Second, reflections fromobjects in the vicinity of the transmitter and receiver can cause apulse that was supposed to be at the beginning of the time window, toappear in at the end of time window, or even in the time window of asubsequent pulse.

As a result, it would be advantageous if the data stream to betransmitted could be encoded by changing a shape of the UWB pulse ratherthan a position of the UWB pulse as with conventional systems. Forexample, if the UWB pulses had two possible shapes, a single time framecould be used encode a single bit of data, rather than the two timeframes (i.e., early and late) that would be required by a PPM system. Inthe present UWB communications system, and related co-pendingapplication Ser. No. 09/209,460 filed May 14, 1998, entitled ULTRA WIDEBANDWIDTH SPREAD SPECTRUM COMMUNICATIONS SYSTEM, information is carriedby the shape of the pulse, or the shape in combination with its positionin the pulse-sequence.

Conventional techniques for generating pulses include a variety oftechniques, for example, networks of transmission lines such as thosedescribed in co-pending application Ser. No. 09/209,460 filed May 14,1998, entitled ULTRA WIDE BANDWIDTH SPREAD SPECTRUM COMMUNICATIONSSYSTEM. One of the problems associated with this technique is that thetransmission lines take up sizeable space and accordingly, are notamenable to integration on a monolithic integrated circuit. Given that akey targeted use of UWB systems is for small, handheld mobile devicessuch as personal digital assistants (PDAs) and mobile telephones, spaceis at a premium when designing UWB systems. Furthermore, it is highlydesirable to integrate the entire radio onto a single monolithicintegrated circuit in order to meet the cost, performance, andvolume-production requirements of consumer electronics devices.

A key attribute that must be maintained, however, regardless of how theinformation is carried, is that no tones can be present. In other words,the average power spectrum must be smooth and void of any spikes. Ingenerating these UWB pulse streams, however, non-X ideal deviceperformance can cause tones to pass through to the antenna and to beradiated. In particular, switches, gates, and analog mixers that areused to generate pulses are well known to be non-ideal devices. Forexample, leakage is a problem. A signal that is supposed to be blockedat certain times, for example, can continue to leak through. Similarly,non-ideal symmetry in positive and negative voltages or currentdirections can allow tones be generated or leak through. In anotherexample, the output of a mixer can include not only the desired UTWBpulse stream, but also spikes in the frequency domain at the clockfrequency and its harmonics, as well as other noise, due to leakagebetween the RF, LO, and IF ports. This is problematic since one of thedesign objectives is to generate a pulse stream that will not interferewith other communications systems.

Similar problems to those discussed above regarding transmitters arealso encountered in UWB receivers. Mixers are used in UWB receivers tomix the received signal with matching waveforms so that the datatransmitted may be decoded. As discussed above, the spectral spikes (DCand otherwise) introduced by the non-ideal analog mixers can makedecoding of only moderately weak signals difficult or impossible.

Furthermore, UWB receivers often suffer from leakage of the UWB signaldriving the mixer. These UWB drive signals can radiate into space and bereceived by the antenna where it can jam the desired UWB signal due toits very close proximity and large amplitude. This reception of thedrive signal being used to decode the received signal can thereforecause a self-jamming condition wherein the desired signal becomesunintelligible.

The challenge, then, as presently recognized, is to develop a highlyintegratable approach for generating shape-modulated wavelet sequencesthat can be used in a UWB communications system to encode, broadcast,receive, and decode a data stream. It would be C) advantageous if thedata stream to be transmitted could be encoded by changing a shape ofthe UWB pulse rather than a position of the UWB pulse as withconventional systems.

Furthermore, the challenge is to build such a wavelet generator wherethe smooth power spectrum calculated by using ideal components, isrealized using non-ideal components. In other words, an approach togenerating and receiving UWB waveforms that does not generate unwantedfrequency domain spikes as a by-product, spikes that are prone tointerfere with other communications devices or cause self-jamming, wouldbe advantageous.

It would also be advantageous if the UWB waveform generation approachwere to minimize the power consumption because many of the targetedapplications for UWB communications are in handheld battery-operatedmobile devices.

SUMMARY OF THE INVENTION

Accordingly, one object of this invention is to provide a novel receiverfor use in a UWB communication system that addresses theabove-identified and other problems with conventional devices.

The inventors of the present invention have recognized that byimplementing a two-mixer approach to receiving UWB waveforms, that thenoise leakage from the non-ideal analog mixers can be whitened, therebyavoiding the interference problems caused by conventional single-mixerapproaches. The present inventors have provided a contrarian approach ofsuppressing mixer-created interference by using a second mixer.

These and other objects are achieved according to the present inventionby providing a novel circuit using a two-mixer approach for decoding areceived UWB waveform having a stream of wavelets while canceling theleakage introduced by non-ideal analog mixers and avoiding self-jamming.

In one embodiment, the UWB receiver uses a conventional differentialmixer to mix a received waveform of a sequence of UWB wavelets not witha correlated and synchronized sequence of wavelets as has been done inconventional systems, but rather, with a synchronized n-bit userpolarity code, the same user code that was used to encode the datastream at the UWB transmitter. The n-bit user polarity code is anon-return-to zero code, not wavelets. Accordingly, by mixing thereceived signal with this synchronized code, the received wavelets willbe either passed through the mixer non-inverted (if mixed with a NRZ‘1’), or inverted (if mixed with a NRZ ‘0’). As a result, the output ofthe first differential mixer is a waveform that has sequences of nwavelets, all in an upright orientation, or all in an invertedorientation, according to the data stream transmitted. The UWB receiverhas a synchronized UWB wavelet generator that generates waveletsaccording to the same shape coding that was used by the transmitter,except always having the same polarity. The output of this receiverwavelet generator is mixed with the output signal of the first mixerusing a second mixer. The output of the second differential mixer willbe a waveform that has sequences of coherently detected wavelets, whereeach group of n wavelets has only positive components (e.g.,corresponding to a data ‘1’), or only negative components (e.g.,corresponding to a data ‘0’), depending on the data being sent. Theoutput waveform has this characteristic because mixing apositive-negative wavelet with itself will produce a positive—positivewavelet, and conversely, mixing a positive-negative wavelet with aninverted representation of itself (i.e., a negative-positive wavelet)will result in a negative—negative wavelet. These all-positive orall-negative wavelets are then integrated and sampled in order to decodethe transmitted data stream.

The inventors of the present invention have recognized that by using twonon-ideal mixers, the interference produced by the first mixer due toimbalance, non-linearity, and leakage between ports, is whitened (i.e.,spread over a wide range) by mixing it's output with the output of thewavelet generator. Furthermore, by mixing the received waveform with aNRZ user code, the present inventors have recognized that leakage (e.g.,radiated through the air and coupled into the receive antenna, orcoupled via the substrate or wiring due to the close proximity of partsin a miniaturized radio) from the wavelet generator in the receiver iswhitened because it is no longer coherent to itself by the time itreaches the second mixer. Instead, the coupled leakage becomespseudo-randomly inverted and non-inverted in the first mixer by the NRZcode such that its contribution to the output of the second mixerintegrates toward zero in the integrator. Furthermore, any similarleakage of the NRZ user code could self-mix to produce a positive ornegative output at the first mixer. This low frequency component,however, is blocked by a coupling network between the two mixers, shown,for example, as a DC blocking capacitor in FIG. 4. Both these forms ofleakage are particularly troubling since they dynamically change withthe environment, which affects the coupling. Finally, the leakage fromthe NRZ signal that passes through the second mixer, plus the leakage ofthe wavelet driving the second mixer, tend to be zero-mean and spiky,but most importantly are synchronized with the integrator and A/Dtiming. As a result, the error is constant and can be estimated andremoved by the receiver controller and interface, by a servo-loop thatsets the A/D zero-reference voltage, or by setting up the coding so asto add and subtract chips such that these leakage terms cancel.

In one embodiment, the conventional mixer is a Gilbert cell mixer. Inother embodiments, the mixer is, for example, a diode bridge mixer, orany electrically, optically, or mechanically-driven configuration ofswitching devices including, for example, an FET, a bulk semiconductordevice, or a micro-machine device.

Consistent with the title of this section, the above summary is notintended to be an exhaustive discussion of all the features orembodiments of the present invention. A more complete, although notnecessarily exhaustive description of the features and embodiments ofthe invention is found in the section entitled “DESCRIPTION OF THEPREFERRED EMBODIMENTS” as well as the entire document generally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a block diagram of an ultra-wide band (UWB) transceiver,according to the present invention;

FIG. 1 b is a diagram for illustrating the operation of the transceiverof FIG. 1 a, according to the present invention;

FIG. 2 is a block diagram of the transceiver of FIG. 1 a, thatmanipulates a shape of UWB pulses, according to the present invention;

FIG. 3 is a schematic diagram of a general-purpose microprocessor-basedor digital signal processor-based system, which can be programmed by askilled programmer to implement the features of the present invention;

FIG. 4 is a schematic diagram of an ultra wideband receiver and waveformcorrelator according to one embodiment of the present invention;

FIG. 5 is an exemplary timing chart illustrating the signals at thevarious inputs and outputs of the components in FIG. 4;

FIG. 6A is a schematic diagram of a generalized single stage mixingcircuit susceptible to self-jamming; and

FIG. 6B is a schematic diagram of a generalized two-stage mixing circuitfor avoiding self-noise in an ultra wideband receiver according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a is a block diagram of an ultra-wide band (UWB) transceiver. InFIG. 1 a, the transceiver includes three major components, namely,receiver 11, radio controller and interface 9, and transmitter 13.Alternatively, the system may be implemented as a separate receiver 11and radio controller and interface 9, and a separate transmitter 13 andradio controller and interface 9. The radio controller and interface 9serves as a media access control (MAC) interface between the UWBwireless communication functions implemented by the receiver 11 andtransmitter 13 and applications that use the UWB communications channelfor exchanging data with remote devices.

The receiver 11 includes an antenna 1 that converts a UWBelectromagnetic waveform into an electrical signal (or optical signal)for subsequent processing. The UWB signal is generated with a sequenceof shape-modulated wavelets, where the occurrence times of theshape-modulated wavelets may also be modulated. For analog modulation,at least one of the shape control parameters is modulated with theanalog signal. More typically, the wavelets take on M possible shapes.Digital information is encoded to use one or a combination of the Mwavelet shapes and occurrence times to communicate information.

In one embodiment of the present invention, each wavelet communicatesone bit, for example, using two shapes such as bi-phase. In otherembodiments of the present invention, each wavelet may be configured tocommunicate nn bits, where M≧2^(nn). For example, four shapes may beconfigured to communicate two bits, such as with quadrature phase orfour-level amplitude modulation. In another embodiment of the presentinvention, each wavelet is a “chip” in a code sequence, where thesequence, as a group, communicates one or more bits. The code can beM-ary at the chip level, choosing from M possible shapes for each chip.

At the chip, or wavelet level, embodiments of the present inventionproduce UWB waveforms. The UWB waveforms are modulated by a variety oftechniques including but not limited to: (i) bi-phase modulated signals(+1, −1), (ii) multilevel bi-phase signals (+1, −1, +a1, −a1, +a2, −a2,. . . , +aN, −aN), (iii) quadrature phase signals (+1, −1, +j, j), (iv)multi-phase signals (1, −1, exp(+jπ/N), exp(−jπ/N), exp(+jπ2/N),exp(−jπ2/N), . . . , exp(+j(N−1)/N), exp(−jπ(N−1)/N)), (v) multilevelmulti-phase signals (a_(i) exp(j2πβ/N)|a_(i)ε{1, a1, a2, . . . , aK},βε(0, 1, . . . , N−1)), (vi) frequency modulated pulses, (vii) pulseposition modulation (PPM) signals (possibly same shape pulse transmittedin different candidate time slots), (viii) M-ary modulated waveformsg_(B) _(i) (t) with B_(i)ε{1, . . . , M}, and (ix) any combination ofthe above waveforms, such as multi-phase channel symbols transmittedaccording to a chirping signaling scheme. The present invention,however, is applicable to variations of the above modulation schemes andother modulation schemes (e.g., as described in Lathi, “Modem Digitaland Analog Communications Systems,” Holt, Rinehart and Winston, 1998,the entire contents of which is incorporated by reference herein), aswill be appreciated by those skilled in the relevant art(s).

Some exemplary waveforms and characteristic equations thereof will nowbe described. The time modulation component, for example, can be definedas follows. Let t_(i) be the time spacing between the (i−1)^(th) pulseand the i^(th) pulse. Accordingly, the total time to the i^(th) pulse is$T_{i} = {\sum\limits_{j = 0}^{i}{t_{j}.}}$The signal T_(i) could be encoded for data, part of a spreading code oruser code, or some combination thereof. For example, the signal T_(i)could be equally spaced, or part of a spreading code, where T_(i)corresponds to the zero-crossings of a chirp, i.e., the sequence ofT_(i)'s, and where $T_{i} = \sqrt{\frac{i - a}{k}}$for a predetermined set of a and k. Here, a and k may also be chosenfrom a finite set based on the user code or encoded data.

An embodiment of the present invention can be described using M-arymodulation. Equation 1 below can be used to represent a sequence ofexemplary transmitted or received pulses, where each pulse is a shapemodulated UWB wavelet, g_(B) _(i) (t−T_(i)). $\begin{matrix}{{x(t)} = {\sum\limits_{i = 0}^{\infty}{g_{B_{i}}\left( {t - T_{i}} \right)}}} & (1)\end{matrix}$

In the above equation, the subscript i refers to the i^(th) pulse in thesequence of UWB pulses transmitted or received. The wavelet function ghas M possible shapes, and therefore B_(i) represents a mapping from thedata, to one of the M-ary modulation shapes at the i^(th) pulse in thesequence. The wavelet generator hardware (e.g., the UWB waveformgenerator 17) has several control lines (e.g., coming from the radiocontroller and interface 9) that govern the shape of the wavelet.Therefore, B_(i) can be thought of as including a lookup-table for the Mcombinations of control signals that produce the M desired waveletshapes. The encoder 21 combines the data stream and codes to generatethe M-ary states. Demodulation occurs in the waveform correlator 5 andthe radio controller and interface 9 to recover to the original datastream. Time position and wavelet shape are combined into the pulsesequence to convey information, implement user codes, etc.

In the above case, the signal is comprised of wavelets from i=1 toinfinity. As i is incremented, a wavelet is produced. Equation 2 belowcan be used to represent a generic wavelet pulse function, whose shapecan be changed from pulse to pulse to convey information or implementuser codes, etc.g _(B) _(i) (t)=re(B _(i,1))·f _(B) _(i,2) _(,B) _(i,3) _(, . . .)(t)+Im(B _(i,1))·h _(B) _(i,2) _(,B) _(i,3) _(, . . .) (t)

In the above equation, function f defines a basic wavelet shape, andfunction h is simply the Hilbert transform of the function f. Theparameter B_(i,1) is a complex number allowing the magnitude and phaseof each wavelet pulse to be adjusted, i.e., B_(i,1)=a_(i)∠θ_(i), wherea₁ is selected from a finite set of amplitudes and θ_(i) is selectedfrom a finite set of phases. The parameters {B_(i,2), B_(i,3), . . . }represent a generic group of parameters that control the wavelet shape.

An exemplary waveform sequence x(t) can be based on a family of waveletpulse shapes f that are derivatives of a Guassian waveform as defined byEquation 3 below. $\begin{matrix}{{f_{B_{i}}(t)} = {{\Psi\left( {B_{i,2},B_{i,3}} \right)}\left( {\frac{\mathbb{d}^{B_{i,3}}}{\mathbb{d}t^{B_{i,3}}}{\mathbb{e}}^{- {\lbrack{B_{i,2}t}\rbrack}^{2}}} \right)}} & (3)\end{matrix}$

In the above equation, the function Ψ( ) normalizes the peak absolutevalue of f_(B) _(i) (t) to 1. The parameter B_(i,2) controls the pulseduration and center frequency. The parameter B_(i,3) is the number ofderivatives and controls the bandwidth and center frequency.

Another exemplary waveform sequence x(i) can be based on a family ofwavelet pulse shapes f that are Gaussian weighted sinusoidal functions,as described by Equation 4 below.f _(B) _(i,1) _(,B) _(i,3) _(,B) _(i,4) =f _(ω) _(i) _(,k) _(i) _(,b)_(i) (t)=e ^(−[b) ^(i) ^(i]) ² sin (ω_(i) t+k _(i) t ²)  (4)

In the above equation, b_(i) controls the pulse duration, ad controlsthe center frequency, and k_(i) controls a chirp rate. Other exemplaryweighting functions, beside Gaussian, that are also applicable to thepresent invention include, for example, Rectangular, Hamming, Hamming,Blackman-Harris, Nutall, Taylor, Kaiser, Chebychev, etc.

Another exemplary waveform sequence x(t) can be based on a family ofwavelet pulse shapes f that are inverse-exponentially weightedsinusoidal functions, as described by Equation 5 below. $\begin{matrix}{{g_{B_{i}}(t)} = {\left( {\frac{1}{{\mathbb{e}}^{\frac{- {({t - {t1}_{i}})}}{{.3}^{*}b_{1}} + 1}} - \frac{1}{{\mathbb{e}}^{\frac{- {({t - {t2}_{i}})}}{{.3}^{*}{tf}_{1}} + 1}}} \right) \cdot {\sin\left( {\theta_{i} + {\omega_{i}t} + {k_{i}t^{2}}} \right)}}} & (5)\end{matrix}$

-   -   where        {B_(i,2), B_(i,3), B_(i,4), B_(i,5), B_(i,6), B_(i,7),        B_(i,8)}={t=t₁ _(i) ,t₂ _(i) , t_(r) _(i) , t_(f) _(i) , θ_(i),        ω_(i), k_(i)}

In the above equation, the leading edge turn on time is controlled byt₁, and the turn-on rate is controlled by t_(r). The trailing edgeturn-off time is controlled by 12, and the turn-off rate is controlledby t_(f). Assuming the chirp starts at t=0 and T_(D) is the pulseduration, the starting phase is controlled by θ, the starting frequencyis controlled by ω, the chirp rate is controlled by k, and the stoppingfrequency is controlled by ω+kT_(D). An example assignment of parametervalues is w=1, t_(r)=t_(f)=0.25, t₁=t_(r)/0.51, and t₂=T_(D)−t_(r)/9.

A feature of the present invention is that the M-ary parameter set usedto control the wavelet shape is chosen so as to make a UWB signal,wherein the center frequency f_(c) and the bandwidth B of the powerspectrum of g(t) satisfies 2f_(c)>B>0.25f_(c). It should be noted thatconventional equations define in-phase and quadrature signals (e.g.,often referred to as 1 and Q) as sine and cosine terms. An importantobservation, however, is that this conventional definition is inadequatefor UWB signals. The present invention recognizes that use of suchconventional definition may lead to DC offset problems and inferiorperformance.

Furthermore, such inadequacies get progressively worse as the bandwidthmoves away from 0.25f_(c) and toward 2f_(c). A key attribute of theexemplary wavelets (or e.g., those described in co-pending U.S. patentapplication Ser. No. 09/209,460) is 7 at the parameters are chosen suchthat neither f nor h in Equation 2 above has a DC component, yet f and hexhibit the required wide relative bandwidth for UWB systems.

Similarly, as a result of B>0.25f_(c), it should be noted that thematched filter output of the UWB signal is typically only a few cycles,or even a single cycle. For example, the parameter n in Equation 3 abovemay only take on low values such as those described in co-pending U.S.patent application Ser. No. 09/209,460).

The compressed (i.e., coherent matched filtered) pulse width of a UWBwavelet will now be defined with reference to FIG. 1 b. In FIG. 1 b, thetime domain version of the wavelet thus represents g(t) and the Fouriertransform (FT) version is represented by G(ω). Accordingly, the matchedfilter is represented as G*(ω), the complex conjugate, so that theoutput of the matched filter is P(ω)=G(ω)·G*(ω). The output of thematched filter in the time domain is seen by performing an inverseFourier transform (IFT) on P(ω) so as to obtain p(t), the compressed ormatched filtered pulse. The width of the compressed pulse p(t) isdefined by T_(C), which is the time between the points on the envelopeof the compressed pulse E(t) that are 6 dB below the peak thereof, asshown in FIG. 1 b. The envelope waveform E(t) may be determined byEquation 6 below. $\begin{matrix}{{E(t)} = \sqrt{\left( {p(t)} \right)^{2} + \left( {p^{H}(t)} \right)^{2}}} & (6)\end{matrix}$

-   -   where p^(H)(t) is the Hilbert transform of p(t).

Accordingly, the above-noted parameterized waveforms are examples of UWBwavelet functions that can be controlled to communicate information witha large parameter space for making codes with good resultingautocorrelation and cross-correlation functions. For digital modulation,each of the parameters is chosen from a predetermined list according toan encoder that receives the digital data to be communicated. For analogmodulation, at least one parameter is changed dynamically according tosome function (e.g., proportionally) of the analog signal that is to becommunicated.

Referring back to FIG. 1 a, the electrical signals coupled in throughthe antenna 1 are passed to a radio front end 3. Depending on the typeof waveform, the radio front end 3 processes the electric signals sothat the level of the signal and spectral components of the signal aresuitable for processing in the UWB waveform correlator 5. The UWBwaveform correlator 5 correlates the incoming signal (e.g., as modifiedby any spectral shaping, such as a matched filtering, partially matchedfiltering, simply roll-off, etc., accomplished in front end 3) withdifferent candidate signals generated by the receiver 11, so as todetermine when the receiver 11 is synchronized with the received signaland to determine the data that was transmitted.

The timing generator 7 of the receiver 11 operates under control of theradio controller and interface 9 to provide a clock signal that is usedin the correlation process performed in the UWB waveform correlator 5.Moreover, in the receiver 11, the UWB waveform correlator 5 correlatesin time a particular pulse sequence produced at the receiver 11 with thereceive pulse sequence that was coupled in through antenna 1 andmodified by front end 3. When the two such sequences are aligned withone another, the UWB waveform correlator 5 provides high signal to noiseratio (SNR) data to the radio controller and interface 9 for subsequentprocessing. In some circumstances, the output of the UWB waveformcorrelator 5 is the data itself. In other circumstances, the UWBwaveform correlator 5 simply provides an intermediate correlationresult, which the radio controller and interface 9 uses to determine thedata and determine when the receiver 11 is synchronized with theincoming signal.

In some embodiments of the present invention, when synchronization isnot achieved (e.g., during a signal acquisition mode of operation), theradio controller and interface 9 provides a control signal to thereceiver 11 to acquire synchronization. In this way, a sliding of acorrelation window within the UWB waveform correlator 5 is possible byadjustment of the phase and frequency of the output of the timinggenerator 7 of the receiver 11 via a control signal from the radiocontroller and interface 9. The control signal causes the correlationwindow to slide until lock is achieved. The radio controller andinterface 9 is a processor-based unit that is implemented either withhard wired logic, such as in one or more application specific integratedcircuits (ASICs) or in one or more programmable processors.

Once synchronized, the receiver 11 provides data to an input port (“RXData In”) of the radio controller and interface 9. An external process,via an output port (“RX Data Out”) of the radio controller and interface9, may then use this data. The external process may be any one of anumber of processes performed with data that is either received via thereceiver 11 or is to be transmitted via the transmitter 13 to a remotereceiver.

During a transmit mode of operation, the radio controller and interface9 receives source data at an input port (“TX Data In”) from an externalsource. The radio controller and interface 9 then applies the data to anencoder 21 of the transmitter 13 via an output port (“TX Data Out”). Inaddition, the radio controller and interface 9 provides control signalsto the transmitter 13 for use in identifying the signaling sequence ofUWB pulses. In some embodiments of the present invention, the receiver11 and the transmitter 13 functions may use joint resources, such as acommon timing generator and/or a common antenna, for example. Theencoder 21 receives user coding information and data from the radiocontroller and interface 9 and preprocesses the data and coding so as toprovide a timing input for the UWB waveform generator 17, which producesUWB pulses encoded in shape and/or time to convey the data to a remotelocation.

The encoder 21 produces the control signals necessary to generate therequired modulation. For example, the encoder 21 may take a serial bitstream and encode it with a forward error correction (FEC) algorithm(e.g., such as a Reed Solomon code, a Golay code, a Hamming code, aConvolutional code, etc.). The encoder 21 may also interleave the datato guard against burst errors. The encoder 21 may also apply a whiteningfunction to prevent long strings of “ones” or “zeros.” The encoder 21may also apply a user specific spectrum spreading function, such asgenerating a predetermined length chipping code that is sent as a groupto represent a bit (e.g., inverted for a “one” bit and non-inverted fora “zero” bit, etc.). The encoder 21 may divide the serial bit streaminto subsets in order to send multiple bits per wavelet or per chippingcode, and generate a plurality of control signals in order to affect anycombination of the modulation schemes as described above (and/or asdescribed in Lathi).

The radio controller and interface 9 may provide some identification,such as user ID, etc., of the source from which the data on the inputport (“TX Data In”) is received. In one embodiment of the presentinvention, this user ID may be inserted in the transmission sequence, asif it were a header of an information packet. In other embodiments ofthe present invention, the user ID itself may be employed to encode thedata, such that a receiver receiving the transmission would need topostulate or have a priori knowledge of the user ID in order to makesense of the data. For example, the E) may be used to apply a differentamplitude signal (e.g., of amplitude “f”) to a fast modulation controlsignal to be discussed with respect to FIG. 2, as a way of impressingthe encoding onto the signal.

The output from the encoder 21 is applied to a UWB waveform generator17. The UWB waveform generator 17 produces a UWB pulse sequence of pulseshapes at pulse times according to the command signals it receives,which may be one of any number of different schemes. The output from theUWB generator 17 is then provided to an antenna 15, which then transmitsthe UWB energy to a receiver.

In one UWB modulation scheme, the data may be encoded by using therelative spacing of transmission pulses (e.g., PPM, chirp, etc.). Inother UVWB modulation schemes, the data may be encoded by exploiting theshape of the pulses as described above (and/or as described in Lathi).It should be noted that the present invention is able to combine timemodulation (e.g., such as pulse position modulation, chirp, etc.) withother modulation schemes that manipulate the shape of the pulses.

There are numerous advantages to the above capability, such ascommunicating more than one data bit per symbol transmitted from thetransmitter 13, etc. An often even more important quality, however, isthe application of such technique to implement spread-spectrum,multi-user systems, which require multiple spreading codes (e.g., suchas each with spike autocorrelation functions, and jointly with low peakcross-correlation functions, etc.).

In addition, combining timing, phase, frequency, and amplitudemodulation adds extra degrees of freedom to the spreading codefunctions, allowing greater optimization of the cross-correlation andautocorrelation characteristics. As a result of the improvedautocorrelation and cross-correlation characteristics, the systemaccording to the present invention has improved capability, allowingmany transceiver units to operate in close proximity without sufferingfrom interference from one another.

FIG. 2 is a block diagram of a transceiver embodiment of the presentinvention in which the modulation scheme employed is able to manipulatethe shape and time of the UWB pulses. In FIG. 2, when receiving energythrough the antenna 1, 15 (e.g., corresponding antennas 1 and 15 of FIG.1 a) the energy is coupled in to a transmit/receive (TIR) switch 27,which passes the energy to a radio front end 3. The radio front end 3filters, extracts noise, and adjusts the amplitude of the signal beforeproviding the same to a splitter 29. The splitter 29 divides the signalup into one of N different signals and applies the N different signalsto different tracking correlators 31 ₁-31 _(N). Each of the trackingcorrelators 31 ₁-31 _(N) receives a clock input signal from a respectivetiming generator 7 ₁-7 _(N) of a timing generator module 7, 19, as shownin FIG. 2.

The timing generators 7 ₁-7 _(N), for example, receive a phase andfrequency adjustment signal, as shown in FIG. 2, but may also receive afast modulation signal or other control signal(s) as well. The radiocontroller and interface 9 provides the control signals, such as phase,frequency and fast modulation signals, etc., to the timing generatormodule 7, 19, for time synchronization and modulation control. The fastmodulation control signal may be used to implement, for example, chirpwaveforms, PPM waveforms, such as fast time scale PPM waveforms, etc.

The radio controller and interface 9 also provides control signals to,for example, the encoder 21, the waveform generator 17, the filters 23,the amplifier 25, the T/R switch 27, the front end 3, the trackingcorrelators 31 ₁-31 _(N) (corresponding to the UWB waveform correlator 5of FIG. 1 a), etc., for controlling, for example, amplifier gains,signal waveforms, filter passbands and notch functions, alternativedemodulation and detecting processes, user codes, spreading codes, covercodes, etc.

During signal acquisition, the radio controller and interface 9 adjuststhe phase input of, for example, the timing generator 7 ₁, in an attemptfor the tracking correlator 31 ₁ to identify and the match the timing ofthe signal produced at the receiver with the timing of the arrivingsignal. When the received signal and the locally generated signalcoincide in time with one another, the radio controller and interface 9senses the high signal strength or high SNR and begins to track, so thatthe receiver is synchronized with the received signal.

Once synchronized, the receiver will operate in a tracking mode, wherethe timing generator 7 ₁ is adjusted by way of a continuing series ofphase adjustments to counteract any differences in timing of the timinggenerator 7 ₁ and the incoming signal. However, a feature of the presentinvention is that by sensing the mean of the phase adjustments over aknown period of time, the radio controller and interface 9 adjusts thefrequency of the timing generator 7 ₁ so that the mean of the phaseadjustments becomes zero. The frequency is adjusted in this instancebecause it is clear from the pattern of phase adjustments that there isa frequency offset between the timing generator 7 ₁ and the clocking ofthe received signal. Similar operations may be performed on timinggenerators 7 ₂-7 _(N), so that each receiver can recover the signaldelayed by different amounts, such as the delays caused by multipath(i.e., scattering along different paths via reflecting off of localobjects).

A feature of the transceiver in FIG. 2 is that it includes a pluralityof tracking correlators 31 ₁-31 _(N). By providing a plurality oftracking correlators, several advantages are obtained. First, it ispossible to achieve synchronization more quickly (i.e., by operatingparallel sets of correlation arms to find strong SNR points overdifferent code-wheel segments). Second, during a receive mode ofoperation, the multiple arms can resolve and lock onto differentmultipath components of a signal. Through coherent addition, the UWBcommunication system uses the energy from the different multipath signalcomponents to reinforce the received signal, thereby improving signal tonoise ratio. Third, by providing a plurality of tracking correlatorarms, it is also possible to use one arm to continuously scan thechannel for a better signal than is being received on other arms.

In one embodiment of the present invention, if and when the scanning armfinds a multipath term with higher SNR than another arm that is beingused to demodulate data, the role of the arms is switched (i.e., the armwith the higher SNR is used to demodulate data, while the arm with thelower SNR begins searching). In this way, the communications systemdynamically adapts to changing channel conditions.

The radio controller and interface 9 receives the information from thedifferent tracking correlators 31 ₁-31 _(N) and decodes the data. Theradio controller and interface 9 also provides control signals forcontrolling the front end 3, e.g., such as gain, filter selection,filter adaptation, etc., and adjusting the synchronization and trackingoperations by way of the timing generator module 7, 19.

In addition, the radio controller and interface 9 serves as an interfacebetween the communication link feature of the present invention andother higher level applications that will use the wireless UWBcommunication link for performing other functions. Some of thesefunctions would include, for example, performing range-findingoperations, wireless telephony, file sharing, personal digital assistant(PDA) functions, embedded control functions, location-findingoperations, etc.

On the transmit portion of the transceiver shown in FIG. 2, a timinggenerator 7 ₀ also receives phase, frequency and/or fast modulationadjustment signals for use in encoding a UWB waveform from the radiocontroller and interface 9. Data and user codes (via a control signal)are provided to the encoder 21, which in the case of an embodiment ofthe present invention utilizing time-modulation, passes command signals(e.g., At) to the timing generator 7 ₀ for providing the time at whichto send a pulse. In this way, encoding of the data into the transmittedwaveform may be performed.

When the shape of the different pulses are modulated according to thedata and/or codes, the encoder 21 produces the command signals as a wayto select different shapes for generating particular waveforms in thewaveform generator 17. For example, the data may be grouped in multipledata bits per channel symbol. The waveform generator 17 then producesthe requested waveform at a particular time as indicated by the timinggenerator 7 ₀. The output of the waveform generator is then filtered infilter 23 and amplified in amplifier 25 before being transmitted viaantenna 1, 15 by way of the T/R switch 27.

In another embodiment of the present invention, the transmit power isset low enough that the transmitter and receiver are simply alternatelypowered down without need for the T/R switch 27. Also, in someembodiments of the present invention, neither the filter 23 nor theamplifier 25 is needed, because the desired power level and spectrum isdirectly useable from the waveform generator 17. In addition, thefilters 23 and the amplifier 25 may be included in the waveformgenerator 17 depending on the implementation of the present invention.

A feature of the UWB communications system disclosed, is that thetransmitted waveform x(t) can be made to have a nearly continuous powerflow, for example, by using a high chipping rate, where the waveletsg(t) are placed nearly back-to-back. This configuration allows thesystem to operate at low peak voltages, yet produce ample averagetransmit power to operate effectively. As a result, sub-micron geometryCMOS switches, for example, running at one-volt levels, can be used todirectly drive antenna 1, 15, such that the amplifier 25 is notrequired. In this way, the entire radio can be integrated on a singlemonolithic integrated circuit.

Under certain operating conditions, the system can be operated withoutthe filters 23. If, however, the system is to be operated, for example,with another radio system, the filters 23 can be used to provide a notchfunction to limit interference with other radio systems. In this way,the system can operate simultaneously with other radio systems,providing advantages over conventional devices that use avalanching typedevices connected straight to an antenna, such that it is difficult toinclude filters therein.

The UWB transceiver of FIG. 1 a or 2 may be used to perform a radiotransport function for interfacing with different applications as partof a stacked protocol architecture. In such a configuration, the UWBtransceiver performs signal creation, transmission and receptionfunctions as a communications service to applications that send data tothe transceiver and receive data from the transceiver much like a wiredI/O port. Moreover, the UWB transceiver may be used to provide awireless communications function to any one of a variety of devices thatmay include interconnection to other devices either by way of wiredtechnology or wireless technology. Thus, the UWB transceiver of FIG. 1 aor 2 may be used as part of a local area network (LAM connecting fixedstructures or as part of a wireless personal area network (WPANconnecting mobile devices, for example. In any such implementation, allor a portion of the present invention may be conveniently implemented ina microprocessor system using conventional general purposemicroprocessors programmed according to the teachings of the presentinvention, as will be apparent to those skilled in the microprocessorsystems art. Appropriate software can be readily prepared by programmersof ordinary skill based on the teachings of the present disclosure, aswill be apparent to those skilled in the software art

FIG. 3 illustrates a processor system 301 upon which an embodimentaccording to the present invention may be implemented. The system 301includes a bus 303 or other communication mechanism for communicatinginformation, and a processor 305 coupled with the bus 303 for processingthe information. The processor system 301 also includes a main memory307, such as a random access memory (RAM) or other dynamic storagedevice (e.g., dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM(SDRAM), flash RAM), coupled to the bus 303 for storing information andinstructions to be executed by the processor 305. In addition, a mainmemory 307 may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby the processor 305. The system 301 further includes a read only memory(ROM) 309 or other static storage device (e.g., programmable ROM (PROM),erasable PROM (EPROM), and electrically erasable PROM (EEPROM)) coupledto the bus 303 for storing static information and instructions for theprocessor 305. A storage device 311, such as a magnetic disk or opticaldisc, is provided and coupled to the bus 303 for storing information andinstructions.

The processor system 301 may also include special purpose logic devices(e.g., application specific integrated circuits (ASICs)) or configurablelogic devices (e.g, simple programmable logic devices (SPLDs), complexprogrammable logic devices (CPLDs), or re-programmable fieldprogrammable gate arrays (FPGAs)). Other removable media devices (e.g.,a compact disc, a tape, and a removable magneto-optical media) or fixed,high density media drives, may be added to the system 301 using anappropriate device bus (e.g., a small system interface (SCSI) bus, anenhanced integrated device electronics (IDE) bus, or an ultra-directmemory access (DMA) bus). The system 301 may additionally include acompact disc reader, a compact disc reader-writer unit, or a compactdisc juke box, each of which may be connected to the same device bus oranother device bus.

The processor system 301 may be coupled via the bus 303 to a display313, such as a cathode ray tube (CRT) or liquid crystal display (LCD) orthe like, for displaying information to a system user. The display 313may be controlled by a display or graphics card. The processor system301 includes input devices, such as a keyboard or keypad 315 and acursor control 317, for communicating information and command selectionsto the processor 305. The cursor control 317, for example, is a mouse, atrackball, or cursor direction keys for communicating directioninformation and command selections to the processor 305 and forcontrolling cursor movement on the display 313. In addition, a printermay provide printed listings of the data structures or any other datastored and/or generated by the processor system 301.

The processor system 301 performs a portion or all of the processingsteps of the invention in response to the processor 305 executing one ormore sequences of one or more instructions contained in a memory, suchas the main memory 307. Such instructions may be read into the mainmemory 307 from another computer-readable medium, such as a storagedevice 311. One or more processors in a multi-processing arrangement mayalso be employed to execute the sequences of instructions contained inthe main memory 307. In alternative embodiments, hard-wired circuitrymay be used in place of or in combination with software instructions.Thus, embodiments are not limited to any specific combination ofhardware circuitry and software.

As stated above, the processor system 301 includes at least one computerreadable medium or memory programmed according to the teachings of theinvention and for containing data structures, tables, records, or otherdata described herein. Stored on any one or on a combination of computerreadable media, the present invention includes software for controllingthe system 301, for driving a device or devices for implementing theinvention, and for enabling the system 301 to interact with a humanuser. Such software may include, but is not limited to, device drivers,operating systems, development tools, and applications software. Suchcomputer readable media further includes the computer program product ofthe present invention for performing all or a portion (if processing isdistributed) of the processing performed in implementing the invention.

The computer code devices of the present invention may be anyinterpreted or executable code mechanism, including but not limited toscripts, interpretable programs, dynamic link libraries, Java or otherobject oriented classes, and complete executable programs. Moreover,parts of the processing of the present invention may be distributed forbetter performance, reliability, and/or cost.

The term “computer readable medium” as used herein refers to any mediumthat participates in providing instructions to the processor 305 forexecution. A computer readable medium may take many forms, including butnot limited to, non-volatile media, volatile media, and transmissionmedia. Non-volatile media includes, for example, optical, magneticdisks, and magneto-optical disks, such as the storage device 311.Volatile media includes dynamic memory, such as the main memory 307.Transmission media includes coaxial cables, copper wire and fiberoptics, including the wires that comprise the bus 303. Transmissionmedia may also take the form of acoustic or light waves, such as thosegenerated during radio wave and infrared data communications.

Common forms of computer readable media include, for example, harddisks, floppy disks, tape, magneto-optical disks, PROMs (EPROM, EEPROM,Flash EPROM), DRAM, SRAM, SDRAM, or any other magnetic medium, compactdisks (e.g., CD-ROM), or any other optical medium, punch cards, papertape, or other physical medium with patterns of holes, a carrier wave,carrierless transmissions, or any other medium from which a system canread.

Various forms of computer readable media may be involved in providingone or more sequences of one or more instructions to the processor 305for execution. For example, the instructions may initially be carried ona magnetic disk of a remote computer. The remote computer can load theinstructions for implementing all or a portion of the present inventionremotely into a dynamic memory and send the instructions over atelephone line using a modem. A modem local to system 301 may receivethe data on the telephone line and use an infrared transmitter toconvert the data to an infrared signal. An infrared detector coupled tothe bus 303 can receive the data carried in the infrared signal andplace the data on the bus 303. The bus 303 carries the data to the mainmemory 307, from which the processor 305 retrieves and executes theinstructions. The instructions received by the main memory 307 mayoptionally be stored on a storage device 311 either before or afterexecution by the processor 305.

The processor system 301 also includes a communication interface 319coupled to the bus 303. The communications interface 319 provides atwo-way UWB data communication coupling to a network link 321 that isconnected to a communications network 323 such as a local network (LAN)or personal area network (PAN) 323. For example, the communicationinterface 319 may be a network interface card to attach to any packetswitched UWB-enabled personal area network (PAN) 323. As anotherexample, the communication interface 319 may be a UWB accessibleasymmetrical digital subscriber line (ADSL) card, an integrated servicesdigital network (ISDN) card, or a modem to provide a data communicationconnection to a corresponding type of communications line. Thecommunications interface 319 may also include the hardware to provide atwo-way wireless communications coupling other than a UWB coupling, or ahardwired coupling to the network link 321. Thus, the communicationsinterface 319 may incorporate the UWB transceiver of FIG. 2 as part of auniversal interface that includes hardwired and non-UWB wirelesscommunications coupling to the network link 321.

The network link 321 typically provides data communication through oneor more networks to other data devices. For example, the network link321 may provide a connection through a LAN to a host computer 325 or todata equipment operated by a service provider, which provides datacommunication services through an IP (Internet Protocol) network 327.Moreover, the network link 321 may provide a connection through a PAN323to a mobile device 329 such as a personal digital assistant (PDA) laptopcomputer, or cellular telephone. The LAN/PAN communications network 323and IP network 327 both use electrical, electromagnetic or opticalsignals that carry digital data streams. The signals through the variousnetworks and the signals on the network link 321 and through thecommunication interface 319, which carry the digital data to and fromthe system 301, are exemplary forms of carrier waves transporting theinformation. The processor system 301 can transmit notifications andreceive data, including program code, through the network(s), thenetwork link 321 and the communication interface 319.

The encoder 21 and waveform generator 17 of the transceiver of thepresent invention function together to create a UWB waveform from adigital data stream by first, multiplying each bit of data in the datastream by an identifying code (e.g., an n-bit user code), therebyexpanding each bit of data into a codeword of data bits equal in lengthto the length of the identifying code. In one embodiment, the codewordis then further processed to create two derivative codewords that arethat are sent to the UWB waveform generator 17 where they are mixed witha pulse generator and recombined through a two-stage mixing processprior to being transmitted via the antenna 15.

As stated above, the encoder 21 receives a digital data stream from anexternal source via the radio and controller interface 9. The encoder 21multiplies each bit of the digital data stream by a user code, which inone embodiment is a unique sequence of bits corresponding to aparticular user. For example, multiplying a user code of ‘1101 0110’ bya data bit of ‘1’ results in an 8-bit representation of the ‘l’ that isidentical to the user code, or ‘1101 0110.’ On the other hand,multiplying that same user code by a data bit of ‘0’ results in an 8-bitrepresentation of the ‘0’ that is the 8 bits of the user code inverted,or ‘0010 1001.’

Continuing with the above example, the encoder 21 multiplies the usercode by each bit of the digital data stream to create a sequence ofn-bit codewords, where n is the length of the user code. Once thedigital data stream has been encoded, the UWB waveform generator 17further processes the sequence of codewords in creating an UWB waveformthat can be transmitted.

FIG. 4 illustrates the details of the UWB waveform correlator 31 of FIG.2, according to the present invention. FIG. 5 is a timing diagramcorresponding to the signals discussed with respect to FIG. 4. As shownin FIG. 4, a propagated signal S1 is coupled to the antenna 1, 15, andis amplified and filtered by the front end 3. The front end 3 outputs asignal S2, which is input to a first mixer 31 a. The first mixer 31 amixes the incoming signal S2 with a Code A signal to produce an outputsignal S3. The signal S3 passes through a simple DC blocking capacitor31 b, or other DC blocking filter network which will block any DC biascomponent of the signal S3, resulting in a new signal S4. The signal S4is mixed via mixer 31 c with a sequence of UWB wavelets W from thewavelet generator 31 e. The wavelet generator 31 e is triggered by thesignal 322/422 of the timing generator 7 to generate the UWB wavelets W.The output of the mixer 31 c is signal S5, which may include a DCcomponent. Signal S5 is passed to an integrator 31 d. The integrator 31d integrates signal S5 for a predetermined number of clock pulses,outputting signal S6, as shown in FIG. 5. In the exemplary timingdiagram of FIG. 5, the integrator has integrated signal S5 for fourclock pulses, resulting in an output level signal S6 of four volts.

After the predetermined number of clock pulses (e.g., four in theexample shown in FIG. 5), the integrator 31 d is reset by the signalReset I. After being reset, the integrator 31 d continues to integratesignal S5 for a second predetermined number of clock pulses. Continuingwith the example of FIG. 5, the integrator 31 d will continue tointegrate the signal S5 for three clock pulses from the point indicatedas A1 in FIG. 5 to the point indicated as A2. Since the signal S5 beingintegrated is made up of negative-amplitude small pulses for the periodof time beginning at point A1 and ending at point A2, the integrator 31d will integrate down for those three clock pulses, as shown by signalS6 of FIG. 5. In this example the resultant output level signal S6 is −3volts.

As shown in FIG. 5, the A/D converter 31 g samples the signal S6 afterboth the first predetermined number of clock pulses (e.g., the firstfour clock pulses) indicated as point A1 in FIG. 5, and after the secondpredetermined number of clock pulses (e.g., the second three clockpulses) indicated as point A2 in FIG. 5. In a similar manner the A/Dconverter 31 g continues to sample the signal S6 at points A3, A4, andso on. The output of the A/D converter 31 g is signal S7, which ismultiplied with a Code B signal by a digital multiplier 31 h. As shownin the exemplary timing diagram shown in FIG. 5, the Code B signal isused to invert the signal S7 for every second sample (i.e., the signalS6 sampled at points A2 and A4 where the integrator had integratednegative amplitude pulses). A summer 31 i sums, for example, twoconsecutive samples (e.g., M=2) on the signal S7 corresponding to thepoints A1 and A2 (or A3 and A4) shown in FIG. 5.

Accordingly, the signal S9 is the result of the signal S6 sampled at thepoint A1 multiplied by +1, plus the signal S6 sampled at the point A2multiplied by −1 (i.e., S9=+1×A1+-1×A2). Latch 31 j latches the value ofsignal S9 as signal S 10, then summer 31 i is reset via signal Reset S.The latch 31 j ensures proper alignment of the signal S10, which isprovided to the radio controller and interface 9.

Control signals (indicated as “Control” in FIG. 4) are also provided tothe waveform correlator 31 from the radio controller and interface 9.The Control signals communicate the parameters (e.g., code length, codevalues, etc.) of the actual codes generated by the code generator 31 f(e.g., Code A, Code B, Xmit Code, etc.). A transmit code, Xmit Code, isshown, for example, as a seven-bit length code in FIG. 5. The Controlsignals also program the wavelet generator 31 e via the code generator31 f for different wavelet styles (e.g., odd symmetry, even symmetry,different center frequency wavelets, different amplitudes, differentphases, wavelet width, etc). The control signals can also program codeB, for example, to always be a positive value (e.g., +1), and the A/Dconverter 31 g and integrator 31 d to integrate and sample only once perbit. In this example, the digital multiplier 31 h and summer 31 i wouldnot be required since the signal S7 would always be multiplied by +1(i.e., S8=+1×S7). The control signals might also program code B, forexample, to be an L-length sequence of plus and minus ones, code A torepeat L times for each bit, and the A/D 31 g and integrator 31 d tointegrate and sample once per Code A repetition. In this way, if Code Awere, for example, an M-length sequence, then a bit would be comprisedof M*L chips.

The benefits of the two-stage mixing technique may be gained throughvarious embodiments of the present invention, as would be understood byone of ordinary skill in the digital signal processing art based on theteachings of the present discussion. The embodiment shown in FIG. 4mixing a user code (Code A) with a received signal at a first mixer 31a, then mixing the output of that first mixer 31 a with the output of awavelet generator (W) is only one exemplary one technique for using atwo-stage mixing approach to eliminate spurious spectral spikes causedby non-ideal analog devices such as the mixers 31 a and 31 c in a UWBreceiver.

As discussed above, a NRZ data source has been encoded prior totransmission with an n-bit user code. As shown in FIGS. 4 and 5, thereceived signal is mixed with Code A at a first mixer 31 a. Code Acorresponds to the first four bits of the user code (Xmit Code) used toencode the data source and the last three bits of the user codeinverted. By inverting a portion of the user code at the receiver, theproblems of self-jamming described in the BACKGROUND OF THE INVENTIONsection, are avoided. Since the signal being supplied to theleakage-prone first mixer 31 a is not the same as the signal that thereceiver is attempting to receive, the problems of self-jamming areavoided, as would be understood by one of ordinary skill in the digitalsignal processing art in light of the present discussion.

FIG. 6A is a schematic diagram of a generalized single stage mixingcircuit for use in an ultra wideband receiver. As shown in FIG. 6A, thereceiver includes an antenna 700, a wavelet generator 701, and mixer702. As discussed above, the receiver of FIG. 6A will be susceptible toself-jamming and self-noise since the output of the wavelet generator701, being mixed with the received signal at mixer 702 has the samecharacteristics as the signal being looked for by the receiver. Due tothe leakage by the mixer 702 the antenna 700 may receive not only thesignal being looked for, but also the leaked signal having similarproperties to the signal being looked for resulting in a self-jamming ofthe receiver.

FIG. 6B is a schematic diagram of a generalized two-stage mixing circuitfor achieving noise cancellation and avoiding self-jamming in an ultrawideband receiver according to the present invention. As shown in FIG.6B, the receiver includes an antenna 703, a de-jam code generator 704, afirst mixer 705, a network 706, a wavelet generator 707, and a secondmixer 708. As discussed above, the present invention uses a two-stagemixing to cancel self-noise caused by the non-ideal analog mixers 705,708 and to avoid self-jamming. The network 706 is used to block any DCbias produced at the first mixer 705. The concepts taught herein provideadvantages to UWB systems regardless of the encoding or modulationscheme being used.

By changing the circuitry of the de-jam code generator 704 and thewavelet generator 707, many different encoding and modulation schemesmay be received, such as those described in co-pending application Ser.No. 09/685,205, entitled SYSTEM AND METHOD FOR GENERATING ULTRA WIDEBANDPULSES. For example, the received UWB wavelets coupled to the antenna700 may, for example, be bi-phase wavelets, multi-level bi-phasewavelets, quad-phase wavelets, multi-level quad-phase wavelets, or othershapes used to encode a NRZ data source at the transmitter. Decoding isachieved by providing the de-jam code generator with the transmit codeused by the transmitter to generate two signals that are mixed with thereceived signals via a two-stage mixing approach.

As described in the context of FIGS. 4 and 5, the receiver can avoidself-jamming by mixing the received waveform with a waveform havingdifferent characteristics than the signal being looked for. As shown inFIG. 6B, the de-jam code generator generates two codes A, B that aremixed with the received signal at the first mixer 705 and the secondmixer 708, respectively. Signal is used to shape the waveletscorresponding to the wavelet shaping scheme used by the transmitter.Wavelet shaping schemes are described in co-pending application Ser. No.09/685,205, entitled SYSTEM AND METHOD FOR GENERATING ULTRA WIDEBANDPULSES. The output generated by the wavelet generator 707 (signal D) ismixed with the received signal at mixer 708. Unlike signal C produced bythe wavelet generator in FIG. 6A, the two signals that are mixed withthe received signal in FIG. 6B (i.e., A and D) are different than thesignal being looked for. Signals A and D that are mixed with thereceived signal have properties such that if A and D were mixedtogether, the resultant waveform would be the same as signal C generatedby the wavelet generator in the single mixer scheme of FIG. 6A.

The de-jam code generator 701 in combination with the wavelet generator704 can implement a variety of schemes for decoding the received UWBwaveform and achieving the advantageous results described herein.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. An ultra wideband receiver that suppresses self-noise, comprising: afirst mixer having a first input, a second input and an output; a secondmixer having a first input coupled to the output of the first mixer, asecond input and an output; a codeword generator configured to generatean n-bit non-return-to-zero codeword having a same predeterminedsequence of bits as an encoding codeword used to encode a transmitteddata stream and invert a predetermined number of bits of the n-bitnon-return-to-zero codeword; and a wavelet generator having an outputcoupled to the second input of the second mixer and configured to outputa sequence of ultra wideband wavelets having a predetermined shape,wherein ultra wideband wavelets received via an antenna coupled to thefirst input of the first mixer, the wavelets having encoded therein thetransmitted data stream encoded with the n-bit non-return-to-zerocodeword, the n-bit non-return-to-zero codeword is input to the secondinput of the first mixer, and the output of the second mixer is adetection waveform having decoded therein the transmitted data stream.2. The receiver of claim 1, further comprising: an integrator having aninput and an output, wherein the output of the second mixer is coupledto the input of the integrator, and a signal output by the integrator isused to decode the transmitted data stream from the detection waveform.3. The receiver of claim 1, further comprising: a network coupledbetween the output of the first mixer and the first input of the secondmixer configured to block a DC component of a signal output by the firstmixer.
 4. A method for suppressing self-noise in an ultra widebandreceiver, comprising the steps of: receiving a received signal of ultrawideband wavelets having encoded therein a transmitted data stream viaan antenna; generating an n-bit non-return-to-zero codeword having asame predetermined sequence of bits as an encoding codeword used by atransmitter for encoding the transmitted data stream, a predeterminednumber of bits of the n-bit non-return-to-zero codeword being inverted;mixing the received signal with the n-bit non-return-to-zero codeword toproduce an intermediate signal; generating an ultra wideband waveletsignal having a sequence of ultra wideband wavelets having a same shapeas ultra wideband wavelets used by the transmitter of the receivedsignal; and mixing the intermediate signal with the ultra widebandwavelet signal to produce a detection waveform.
 5. The method of claim4, further comprising: integrating the detection waveform to decode thetransmitted data stream.
 6. The method of claim 4, further comprising:blocking a DC component of the intermediate signal.
 7. The method ofclaim 4, further comprising: multiplying the integrated detectionwaveform with an adjusting codeword, wherein a product of the n-bitnon-return-to-zero codeword and the adjusting codeword is equivalent toa transmit codeword used to encode the received signal.
 8. The method ofclaim 4, wherein the n-bit non-return-to-zero codeword comprises a firstnon-return-to-zero portion and a second non-return-to-zero portion,wherein the first non-return-to-zero portion has equivalent signalvalues with respect to a corresponding first transmit portion in atransmit codeword used to encode the received signal, and wherein thesecond non-return-to-zero portion has inverse signal values with respectto a corresponding second transmit portion in the transmit codeword. 9.The method of claim 5, wherein the integrating of the detection waveformis performed separately over two or more portions of the detectionwaveform, a combined length of the two or more portions being n-bits.10. A computer program product, comprising: a computer storage medium;and a computer program code mechanism embedded in the computer storagemedium for performing an ultra wideband receiver self-noise suppressingmethod, the computer program code mechanism having a first computer codedevice configured to generate an n-bit non-return-to-zero codewordhaving a same predetermined sequence of bits as an encoding codewordused by a transmitter for encoding a transmitted data stream, apredetermined number of bits of the n-bit non-return-to-zero codewordbeing inverted for mixing with a received signal to produce anintermediate signal; a second computer code device configured togenerate an ultra wideband wavelet signal having a sequence of ultrawideband wavelets having a same shape as ultra wideband wavelets used bythe transmitter of the received signal for mixing with the intermediatesignal to produce a detection waveform.
 11. An ultra wideband receiverthat suppresses self-noise, comprising: a de-jam code generator having afirst input, a first output, and a second output, the first input beingconfigured to receive a transmit code used by an ultra widebandtransmitter, the first output and the second output being configuredsuch that mixing the first output with the second output produces awaveform that correlates to a transmitted waveform being received; afirst mixer having a first input, a second input, and an output, thefirst input being configured to receive a waveform from an antenna, thesecond input being configured to receive the first output from thede-jam code generator; a wavelet generator having an input and anoutput, the input being configured to receive the second output from thede-jam code generator, and the output being configured to generate asequence of ultra wideband wavelets having a predetermined shapecorresponding to an encoding scheme used by the ultra widebandtransmitter; and a second mixer having a first input, a second input andan output, the first input being configured to receive the output of thefirst mixer, the second input being configured to receive the output ofthe wavelet generator, wherein the output of the second mixer is asequence of shaped wavelets having decoded therein non-return-to-zerodata transmitted by the ultra wideband transmitter.
 12. A two-stageultra wideband receiving circuit, comprising: a first stage configuredto mix a received signal with a noise suppression code and generate anintermediate signal: a second stage configured to mix the intermediatesignal with a wavelet to generate an output signal: an integratorconfigured to receive and decode the output signal to provide a decodedsignal; and a multiplier configured to combine the decoded signal withan adjusting code to provide an adjusted signal, wherein the noisesuppression code is the same length as a transmit code used to encodethe received signal, wherein the noise suppressing code differs in valuefrom the transmit code, wherein the integrator integrates the outputsignal separately over two or more portions of the output signal toprovide the decoded signal, and wherein the product of the noisesuppression code and the adjusting code is equivalent to the transmitcode.
 13. A two-stare ultra wideband receiving circuit, comprising: afirst stage configured to mix a received signal with a noise suppressioncode and generate an intermediate signal; and a second stage configuredto mix the intermediate signal with a wavelet to generate an outputsignal, wherein the noise suppression code is the same length as atransmit code used to encode the received signal wherein the noisesuppressing code differs in value from the transmit code, wherein thenoise suppression code comprises a first noise suppression portion and asecond noise suppression portion, wherein the first noise suppressionportion has equivalent signal values with respect to a correspondingfirst transmit portion in the transmit code, and wherein the secondnoise suppression portion has inverse signal values with respect to acorresponding second transmit portion in the transmit code.
 14. Thetwo-stage ultra wideband receiving circuit of claim 13, wherein thesecond noise suppression portion is a contiguous portion of the noisesuppression code.